Said It Here

How to check for a silent toilet tank leak

Silent toilet leaks waste water into the bowl without obvious signs, making it hard to catch before water bills spike or damage occurs. People want a reliable visual indicator, such as a colored or disinfecting block in the cistern, to easily spot continuous leakage without guessing.

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

  1. 1
    Drying the area, pointing a fan at it, and testing with flat toilet paper to see if it wicks moisture.

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.

r/Plumbing2 people · September 2026

I want a block of dye, or a definitely coloured thing, that I can put in the cistern, that I accept will dye (and maybe disinfect or neutralise hard water) every flush, but will also alert me if my cistern is leaking into the bowl.source ↗

blackcurrantcat · r/Plumbing · 2 upvotes

The grout line behind my toilet had this half inch wet looking line.source ↗

Is this an indication of a wax ring leak or possibly just condensation? Really confused.source ↗

kentBis · r/Plumbing · 1 upvotes

Where this came up

People with this problem also raised